Prophett, son of an undertaker, caught the flying bug at a young age. He moved from his east coast hometown to San Diego at the earliest possible age, and enrolled at the Ryan School of Aeronautics, obtaining an aircraft Master Mechanic's License and a pilot's license. There he was able to train with the men that had built Lindbergh's transatlantic aircraft. He became a flight instructor for Ryan, then chief pilot for their commercial flight operations. In World War II he was an air corps pilot instructor. After the war he joined Consolidated Aircraft as a test pilot.

He put a number of Convair's aircraft through their test programs, including late models of the B-24 bomber, the CV-340 and CV-880 airliners, the giant XC-99 transport, and the B-36 and the XB-46 jet bombers. In 1954 he was named Convair's chief of F-102 / F-106 interceptor flight test at Edwards, and later ran tests of those fighters' air-to-air missile systems at Holloman. By 1961 he was Convair's Chief of Engineering Flight Test, and had over 7,000 hours of flight time.

Prophett was moved to the Atlas ICBM program in 1961 to take over the base activation program, which was in crisis. He saw the first ICBM through completion of deployment by 1963, followed by its rapid deactivation. He left the Atlas program in 1966, becoming Convair's director of international sales. Prophett retired in 1977.